Question

A plane glass slab is kept over various colored letters, the letter which appears least raised is?
(A) Violet
(B) Blue
(C) Green
(D) Red

Answer 1

Appearance of the light through-plane glass depends upon the refractive index of the light. The Refractive index of glass is higher than the refractive index of water. The way in which light appears through the glass depends on its refractive index and the wavelength of the light.

Complete step by step answer:
Glass is the dispersive medium in which its refractive index mainly depends on the wavelength of the light that enters it. For the light with the lower wavelengths, the refractive index is greater. It refracts greater in the glass. On the other hand, the light with the greater wavelength has a less refractive index. Thus, these lights refract less. The longer wavelength lights travel through the dispersing medium without any refraction. Hence, it appears much clear than the shorter wavelength lights.
Among the given lights, red light has the maximum wavelength than the other and it can go through the refractive indexes and all the layers without much disturbances. Hence, it moves faster than the other lights. This makes the red light to appear least raised than the others outside the slab.

Thus, the option (D) is correct.

Additional information:
The Refractive index of red light through glass is $1.513$ and that of violet light is $1.532$. Refractive index of blue light is $1.525$ and that of green light is $1.515$. The Refractive index is mainly used in the testing of purity of any products, to find the concentration of any substance.

Note:
The Refractive index is different for different colored lights, also the refractive index may vary based on the medium through which the light passes. The wavelength is another factor that determines the refractive index.